Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $61.74   5.738%   $65.2826   $65.28   $65.30   $65.30  
  Purchase #2 $146.88   3.177%   $151.5464   $151.55   $151.55   $151.50  
  Purchase #3 $179.97   5.136%   $189.2133   $189.21   $189.20   $189.20  
  Purchase #4 $247.99   9.617%   $271.8392   $271.84   $271.85   $271.80  
  Purchase #5 $219.42   8.463%   $237.9895   $237.99   $238.00   $238.00  
  Purchase #6 $218.56   6.583%   $232.9478   $232.95   $232.95   $232.90  
  Purchase #7 $205.83   9.121%   $224.6038   $224.60   $224.60   $224.60  
  7 purchase totals = $1,280.39       $1,373.4226   $1,373.42   $1,373.45   $1,373.30